Generator Questions

[Don Higgins]

I have been battling a 10 K Onan generator that will run all day at times then slowly shut down every 30 minutes at night. The code it generates is 36.

I put a new fuel filter, air filter, checked all tubing for plastic bags and changed the oil and filter. The engine is the Isuzu. The only thing I can say that may help is the fuel pump return line stops pulsing when the engine was about to die. When I pushed the return line over to the side to restrict it the engine sprang back to life.

I think the fuel pump isn't pumping or the board isn't telling the pump to continue pumping. I will replace the pump this week but do you have any other ideas? Slate Cummings was having the exact same problem this week but he replaced the pump and it still slowly dies every 30 minutes.

[Matt Schurman]

Good Morning.

The last two posts require different responses, which will both lead in similar directions. So bear with me, this stuff is work....lol

First, NHRA1285, your code 17 is a fuel pump fault code, which is trigger by the controller unable to sense the electric pump. This is a bypassable fault, which means it can be reset and ignored, but that information is pretty much useless if the machine won't run. When the control doesn't "see" the fuel pump in the circuit, it won't allow the engine to crank, it just drops right into a fault 17, so the fuel pump and wiring needs to be tested.

Your unit is installed without regard for making this type of repair within the confines of a Class A motorcoach. Without seeing the installation I can't say for sure but I'm fairly certain it will have to come out to chase this problem down. It's a big pain and yes, it will probably come out the bottom of the coach. We use a forklift and a great deal of cursing. Give me a call to discuss, I think I can help you more over the phone with some of the details. 800-821-5973

[Matt Schurman]

Don,

Your problem is becoming fairly common for us to see. Replacing the fuel pump is a good place to start, we do some bench testing of the pump to confirm failures but changing it out in the field serves a good purpose. Sometimes it's just a bad fuel pump that goes intermittent.

In some other instances we've seen issues stemming from too much current on the pins of the ECM providing power to the fuel pump. Sometimes the only way to fix it is to replace the ECM AND the pin connection supplying the positive pump signal. That pin can be inspected carefully, if it shows signs of gray/overheat, the problem is identified. We then cut out that wire in the ECM harness and replace it, giving you a nice new connection as well as replacing the ECM, (which gives you a new pin contact)

If you supply me with the model and spec number, I'm certain I can provide you with some diagrams and tech support. 800-821-5973

[a pontiac]

I have a 02 fleeetwood rv onan quiet diesel 7500. The manual says it should have the belt replaced at 1500 hrs. Is this something I can do like other routine maintenance? You guys are providing a great service, thank you.

[Rich Biebel]

The belt on most of those QD 7500's is the water pump drive belt. It has no adjustment. The sheet metal covers need to be removed and in motorhomes that often means the unit has to come out. Since there is no adjustment.....the water pump pulley must be removed to remove and replace the belt. The fit has to be reasonably tight so the right belt is important. The belts crack and if it is not changed could break and the unit will obviously overheat. I usually change the t-stat and temp sensor at the same time. Deposits build up on the sensor and they can cause poor cold starts and random shutdowns. The sensor signals the controller by way of an ohm reading what the coolant temp is and this controls the glow plug operation....If the unit is cold....the glow plugs are powered before cranking.If it is warm they do not energize.

[Mark Lewis]

I have a Onan Marquis 5500, model # 5.5BGMFA26105H.
Do not know the hours on it and it runs good .Unit is at least 13yrs old.
I recently had to replace the fuel pump.
The only issue I have is it seems to get lugged down when I turn the AC on, has a 13500 roof air unit on trailer.
Is there anything that needs to be done to the generator part as far as routine maintenance goes? All I have is a 5 gal hot water heater and microwave besides the ac.

Thanks for the help
Mark Lewis

[Rich Biebel]

Mark......Those older Onans run well and should easily run your AC and other items at the same time. The rated output on a 5500 is about 45 amps at 120 volts. An ac unit probably draws no more than 15 amps and a microwave maybe 10, Hot water heater I would guess another 10 tops so you are well within the generators capability.

The older Onans were flathead engines. 1800rpm. They tend to carbon up heavily inside the cylinder heads and intake ports. The rear intake port often is much worse with that carbon buildup. The engine supplies the power to spin the rotor of the generator. The magnetic field created as load increases is the load the engine sees. So if the engine is weak it cannot "carry the load" of the magnetic field in the generator. There is basically nothing in the generator end to service other than the brushes. They are either good or bad and if they are bad you will not have any AC output and the unit will likely not stay running due to loss of AC output.

The first thing to do is make sure the std tune-up items are good and if the machine has a lot of hours on it......a heads off carbon cleaning might be what it needs. Valve lash is also a big factor that causes them to run weak. Exhaust valves get tight, not enough lash and once the engine is hot they run poorly from improper valve seating. lash is .005 Intake and .013 exhaust cold.

I remove the heads......remove the manifolds.....clean the carbon in the heads and ports and the backs of the valves. Adjust the valve lash and reassemble it.......Carb has to be good.....Governor arm and all adjustments set carefully under load for best operation. I use a resistive load bank on all the units I service and repair. Everyone gets tested and adjusted with no load and right up to full rated load. Carbs are very sensitive on mixture and governor arm adjustments.....

[5848]

I have the chance to purchase a Onan Emerald 1 Genset 4Kw rv generator and was wondering your thoughts on this model? This would go into our race trailer.

[Rich Biebel]

Originally Posted by 5848

I have the chance to purchase a Onan Emerald 1 Genset 4Kw rv generator and was wondering your thoughts on this model? This would go into our race trailer.

They were good units.....but that would be a pretty old unit. They have not made that design for over 10 years. Did it have an hour meter attached to it ? It's always helpful to know the amount of usage on a machine of that vintage. An hour meter is the closest thing to an odometer.

I would not buy one unless it looked to be well cared for and could be tested. It is very easy to run one even if it is not installed in anything.

Add a battery and a gas can and run it and check the output voltage. I run every unit I work on....on a bench and it gets load tested with a resistive load bank to full rated load.....It's a lot of work to install one in a trailer or M-H so it should be confirmed as good before doing an install....

[5848]

The hour meter has 232 hrs on it and the unit does look to be in good condition. What is the noise decibel on one of these units? There are asking $500 for the unit.
Thanks